1. Field of the Invention
The present invention relates to a technique capable of reducing an outline size of a set in a small-sized liquid crystal display device used in a portable telephone or the like.
2. Description of the Related Art
In connection with a liquid crystal display device there is a strong demand for reducing an outline size of a set while keeping a certain screen size. To meet this demand various efforts have been made for narrowing the frame of a liquid crystal panel, improving the accuracy of parts of a liquid crystal panel holder, reducing the holder thickness, improving the accuracy of parts of a metallic frame serving as an outer frame, reducing the thickness of the metallic frame, and reducing the size of a back light structure.
FIG. 12 is a plan view of a portable telephone using a conventional liquid display device. A liquid crystal display panel forms an image by applying a signal voltage for each pixel to liquid crystal held grippingly between an upper glass substrate 1 and a lower glass substrate 2. An upper polarizing plate 3 is affixed to the upper glass substrate. Numeral 4 denotes a holder for accommodating a liquid crystal panel. The holder 4 is usually formed of resin. An IC chip 5 for driving the liquid crystal is mounted on the lower glass substrate 2 of the liquid crystal panel. Numeral 6 denotes a flexible wiring substrate, which supplies for example an electric current to the liquid crystal driving IC chip 5. The flexible wiring substrate 6 is turned back and is integral with a back light provided on the back side of the liquid crystal panel. A combination of the liquid crystal panel, the drive circuit and the back light is called a liquid crystal module, which is accommodated inside a metallic frame 7.
There has been a demand for maintaining an effective screen size and reducing an outline size of a set while maintaining the basic configuration of the liquid crystal display device.
Such a conventional technique is described in the following Patent Literatures: JP-A-2001-133756; JP-A-2004-29651; JP-A-2004-62048; and JP-A-2005-338497.
To reduce the size of a set such as a portable telephone, the following have been adopted: reduction in the size of a liquid crystal module; reduction in the thickness of a metallic frame; and improvement in the assembling accuracy of both liquid crystal module and metallic frame. FIG. 13 is a sectional view taken along line A-A of FIG. 12 showing a conventional example.
In FIG. 13, the same parts as in FIG. 12 are identified by the same reference numerals as in FIG. 12. A lower polarizing plate 8 is affixed to the lower glass substrate 2. The holder 4 is stepped in two stages, with the liquid crystal panel being mounted on the stepped portion. The lower substrate of the liquid crystal panel is bonded to the holder through a double coated light shielding adhesive tape 9. The double coated light shielding adhesive tape not only fixes the liquid crystal panel to the holder but also prevents the entry of light from the back light to the peripheral portion of the liquid crystal screen with a consequent lowering in contact of the screen peripheral portion. Numeral 10 denotes an upper diffusing sheet, numeral 11 denotes an upper prism sheet, numeral 12 denotes a lower prism sheet, numeral 13 denotes a lower diffusing sheet, and numeral 14 denotes a light guide plate. Further, numeral 15 denotes a reflecting plate, which reflects light traveling downward from the light guide plate and causes it to travel toward the liquid crystal panel.
In order to reduce the outline size of the set, assuming that the outline size of the liquid crystal panel is constant, the following can be adopted: for example, reduction in the wall thickness mt of an upper portion of the holder 4 shown in FIG. 13; reduction in the wall thickness ft of the frame 7; narrowing of a gap g1 between the frame 7 and the holder 4; or narrowing of a gap g2 between the liquid crystal panel 1 and the upper portion of the holder 4.
However, a limit is encountered in the abovementioned means. Reducing the wall thickness ft of the frame 7 and reducing the wall thickness mt of the holder upper portion to below respective certain values encounter problems in machining. Moreover, the gap g1 between the frame 7 and the holder 4, as well as the gap g2 between the liquid crystal panel 1 and the holder 4, are required from the standpoint of part tolerance and assembling process. To reduce those sizes, it is necessary to make small the tolerances of the outline sizes of the parts. However, making small the tolerances of the parts concerned leads to a rise of the cost for the parts due to, for example, a lowering of the yield of the parts.